Piezoelectric generator for hydraulic systems

ABSTRACT

The present disclosure generally relates to electrical power generation from a piezoelectric material. A piezoelectric power generator assembly is disclosed including a housing, a piezoelectric transducer located in the housing, and a piston located in the housing, wherein the piezoelectric transducer is configured to generate an electrical charge when contacted by the piston. A piezoelectric power generator assembly is also disclosed including a housing comprising a flowline located within the housing and a piezoelectric transducer located in the housing and disposed about a perimeter of the flowline, wherein the piezoelectric transducer is configured to generate an electrical charge when contacted by a fluid contained in the flowline. A subsea drilling system is disclosed including a subsea blowout preventer stack and a piezoelectric power generator assembly for powering sensors on the blowout preventer stack configured to monitor characteristics of the stack.

BACKGROUND

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the presently describedembodiments. This discussion is believed to be helpful in providing thereader with background information to facilitate a better understandingof the various aspects of the present embodiments. Accordingly, itshould be understood that these statements are to be read in this light,and not as admissions of prior art.

In modern hydrocarbon drilling and production operations, there is anever-increasing need to add more sensors and instrumentation toequipment. However, the installation of additional sensors andinstrumentation with subsea hydrocarbon drilling and productionoperations raises challenges regarding the infrastructure needed tosupply power and handle communications to and from these sensors andinstrumentation. Since subsea conditions can be hostile, minimizing thenumber and size of equipment near a well, such as wires or externalbatteries, is a common objective. Accordingly, there is a need forsubsea electrical power generation to power components on a subseaassembly while minimizing the number and size of additional pieces ofequipment required.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present disclosure are described indetail below with reference to the attached drawing figures, which areincorporated by reference herein and wherein:

FIG. 1 is a schematic view of an example drilling system;

FIG. 2 is a front elevation view of a blowout preventer stack and lowermarine riser package;

FIG. 3 is a cross-sectional view of an embodiment of an in-linepiezoelectric power generator assembly adjacent a valve block;

FIG. 4 is a cross-sectional view of an embodiment of a piezoelectricpower generator assembly exposed to seawater and including aforce-multiplying piston;

FIG. 5 is a top elevation view of an embodiment of a piezoelectric powergenerator assembly exposed to seawater and including a force-multiplyingpiston;

FIG. 6 is a cross-sectional view of an embodiment of a piezoelectricpower generator assembly exposed to seawater and including aforce-multiplying piston and further including a diaphragm; and

FIG. 7 is a cross-sectional view of an embodiment of a piezoelectricpower generator assembly including a force-multiplying piston adjacent aT-piece fitting.

The illustrated figures are only exemplary and are not intended toassert or imply any limitation with regard to the environment,architecture, design, or process in which different embodiments may beimplemented.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following discussion is directed to various embodiments of thepresent disclosure. The drawing figures are not necessarily to scale.Certain features of the embodiments may be shown exaggerated in scale orin somewhat schematic form and some details of conventional elements maynot be shown in the interest of clarity and conciseness. Although one ormore of these embodiments may be preferred, the embodiments disclosedshould not be interpreted, or otherwise used, as limiting the scope ofthe disclosure, including the claims. It is to be fully recognized thatthe different teachings of the embodiments discussed below may beemployed separately or in any suitable combination to produce desiredresults. In addition, one skilled in the art will understand that thefollowing description has broad application, and the discussion of anyembodiment is meant only to be exemplary of that embodiment, and notintended to intimate that the scope of the disclosure, including theclaims, is limited to that embodiment.

Certain terms are used throughout the following description and claimsto refer to particular features or components. As one skilled in the artwill appreciate, different persons may refer to the same feature orcomponent by different names. This document does not intend todistinguish between components or features that differ in name but arethe same structure or function.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. In addition, the terms “axial” and “axially”generally mean along or parallel to a central axis (e.g., central axisof a body or a port), while the terms “radial” and “radially” generallymean perpendicular to the central axis. For instance, an axial distancerefers to a distance measured along or parallel to the central axis, anda radial distance means a distance measured perpendicular to the centralaxis. The use of “top,” “bottom,” “above,” “below,” and variations ofthese terms is made for convenience, but does not require any particularorientation of the components.

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentmay be included in at least one embodiment of the present disclosure.Thus, appearances of the phrases “in one embodiment,” “in anembodiment,” and similar language throughout this specification may, butdo not necessarily, all refer to the same embodiment.

The present disclosure relates generally to electrical power generationand, in an embodiment described herein, more particularly provides apiezoelectric power generator assembly that generates an electricalcharge under mechanical strain. The electrical charge is usable, forinstance, to power electrically operated devices and to charge devices,such as capacitors. The mechanical strain is generated by harnessing thepower of fluids already present at the subsea installation by applyingthese to piezoelectric materials. Piezoelectric power generatorsaccording to this disclosure can be retrofitted to existing equipmentwithout the downside of having to add more cabling to the installation.Sensors and recording of measurements from same is possible duringperiods when subsea equipment, such as a blowout preventer, isdisconnected from the main power supply, such as would happen after anEmergency Disconnect Sequence. The range of monitored situations ofsafety critical equipment, such as blowout preventer, is therebyincreased.

Referring now to FIG. 1, an embodiment of an offshore system 100 fordrilling and/or producing a wellbore 102 is shown. In this embodiment,the system 100 includes an offshore vessel or platform 104 at the seasurface 106 and a subsea blowout preventer (“BOP”) stack assembly 108mounted to a wellhead 110 at the sea floor 112. The platform 104 isequipped with a derrick 114. A tubular drilling riser 116 extends fromthe platform 104 to the BOP stack assembly 108. The drilling riser 116returns drilling fluid or mud to the platform 104 during drillingoperations. One or more hydraulic conduits 118 extend along the outsideof the riser 116 from the platform 104 to the BOP stack assembly 108.The conduits 118 supply pressurized hydraulic fluid to the BOP assembly108.

Referring now to FIGS. 1 and 2, the BOP stack assembly 108 is mounted tothe wellhead 110 and is designed and configured to control and seal thewellbore 102, thereby containing the hydrocarbon fluids (liquids andgases) therein. In this embodiment, the BOP stack assembly 108 comprisesa lower marine riser package (“LMRP”) 202 and a BOP or BOP stack 204.

The BOP stack 204 is releasably secured to the wellhead 110 as well asthe LMRP 202. Likewise, the LMRP 202 is releasably secured to the BOPstack 204 and the riser 116. In this embodiment, the connections betweenthe wellhead 110, the BOP stack 204, and the LMRP 202 includehydraulically actuated, mechanical wellhead-type connections 122. Ingeneral, the connections 122 may comprise any suitable releasablewellhead-type mechanical connection such as the DWHC or HC profilesubsea wellhead system available from Cameron International Corporationof Houston, Tex., or any other such wellhead profile available fromseveral subsea wellhead manufacturers. Typically, such hydraulicallyactuated, mechanical wellhead-type connections (e.g., connections 122)include an upward-facing male connector, or “hub,” that is received byand releasably engages a downward-facing mating female connector orreceptacle. In this embodiment, the connection between LMRP 202 and theriser 116 is a flange connection that is remotely controlled, just asthe connections 122 may be remotely, hydraulically controlled.

The blowout preventer assembly 108 contains hydraulic conduits or piping226 for conveying hydraulic fluid throughout the assembly. In FIG. 2,the illustrated hydraulic conduits 226 are limited in number for ease ofviewing and explanation. However, it is known to those of ordinary skillin the art that a blowout preventer assembly may comprise numeroushydraulic conduits for distributing hydraulic fluid to a number ofpoints on the blowout preventer, such as an actuator (e.g., valve 228).

A cross-section of an example of a piezoelectric power generatorassembly 300 is illustrated in FIG. 3. In the illustrated embodiment,the piezoelectric power generator assembly 300 is disposed in-line witha fluid conduit 302. The fluid conduit 302 can be any type of fluidconduit for conveying a fluid, whether located subsea or at a surfacelocation. In the embodiment illustrated in FIG. 3, the fluid conduit isa hydraulic fluid conduit for conveying pressurized hydraulic fluid on ablowout preventer assembly, such as those illustrated in FIGS. 1 and 2.The piezoelectric power generator assembly 300 is located in-line withthe fluid conduit adjacent a valve block assembly 304. The piezoelectricpower generator assembly 300 includes end fittings 306 for coupling theassembly 300 to end fittings 308 of the fluid conduit 302. Accordingly,the piezoelectric power generator assembly 300 can be retrofitted to anexisting fluid conduit. Alternatively, the piezoelectric power generatorassembly 300 can be integral to the fluid conduit, i.e., installedin-line without end fittings of any kind.

The piezoelectric power generator assembly 300 includes a housing 310.The illustrated housing 310 is shown having a square cross-sectionalprofile. However, other geometries are envisioned. The housing 310includes a flow passage 312 defined within the interior of the housing310 along a longitudinal axis 314 of the housing 310. Pressurizedhydraulic fluid for actuating the valve block assembly 304 travelsthrough the fluid conduit 302, through the flow passage 312, and to thevalve block 304. The pressurized hydraulic fluid can be used to, e.g.,operate a valve member (not shown) disposed within the valve blockassembly 304. Since the piezoelectric power generator assembly 300 isin-line, it does not restrict the flow of the fluid through the conduit302.

The housing 310 includes a piezoelectric transducer 316 composed of apiezoelectric material. Non-limiting examples of suitable piezoelectricmaterials include crystals (such as quartz, Berlinite and Rochelle salt)and ceramics (such as Lead Zirconate Titanate (PZT), Barium Titanate andLithium tantalate). However, any piezoelectric material capable ofaccumulating an electrical charge in response to an applied mechanicalstress can be used. The piezoelectric transducer 316 is disposed aboutthe perimeter of the flow passage 312. Accordingly, the piezoelectrictransducer 316 is exposed to the fluid pressure which applies a stresson the piezoelectric transducer 316 (pressurized hydraulic fluid in asubsea fluid conduit is at a pressure higher than ambient pressure,sometimes several thousand pounds per square inch). As a result of thePiezoelectric Effect, the piezoelectric transducer 316 generates anelectrical charge in response to the stress.

The generated electrical charge can be passed via wires 318 to anyelectrically powered device or to a capacitor bank for storage. Suchelectrically powered devices or capacitors may be local (e.g., on thehousing 310 or valve block assembly 304), or may be remote (e.g., manyfeet or miles away). In the illustrated embodiment, the generatedelectrical charge is passed to an electronics module 320. Theelectronics module 320 includes a capacitor bank 322 for storing thegenerated electricity and a power conditioning unit 324 for improvingthe quality of the electrical power delivered to other devices. Theelectronics module 320 could further include any other componentscommonly used for storing and distributing electricity.

The valve block assembly 304 further includes a sensor unit 326 locatedon top of the valve block assembly 304. The sensor unit 326 could belocated at any location on the valve block assembly 304, or evenremotely relative the valve block assembly 304. The sensor unit 326includes a sensor 328 for measuring characteristics of the valve blockassembly and a storage device 330 capable of receiving and storingsensor 328 measurement data. One suitable sensor is a Hall-Effect sensorwhich could be attached to the outside of the valve block assembly 304.A Hall-Effect sensor would provide for detection of fully open and fullyclosed states of the valve block assembly 304 by detecting the presenceor absence of valve components as they shuttle between positions. Othertypes of sensors could also be incorporated for detecting variouscharacteristics of the valve block assembly 304, such as temperature,pressure, strain, etc. The storage device 330 receives and stores thesensor 328 measurement data. These data can be wirelessly transferred toa remote location (e.g., to the surface if the sensor is subsea) or canbe recovered locally at the sensor (e.g., by a remotely operated vehiclewith corresponding electronics). One of several wireless options isinclusion of a radio frequency identification (“RFID”) chip, or similar.The RFID tag can be incorporated into storage device 330 to allow datafrom sensor 328 to be communicated to a remotely operated vehiclebringing a reading wand into the vicinity of the RFID tag in order tostimulate the tag and download the data. Alternatively, a technician atthe surface using a reading wand can scan the tag to effect a datadownload.

The sensor unit 326 can be powered entirely, or in part, by electricitygenerated by the piezoelectric power generator assembly 300, providingfor a battery-free, independent, locally powered system. Such a systemcould be incorporated anywhere in a surface or subsea drilling orproduction installation where sensing is desired without increasing thecomplexity of the system.

A cross-section of an example of a piezoelectric power generatorassembly 400 is illustrated in FIG. 4. In the illustrated embodiment,the piezoelectric power generator assembly 400 includes a housing 402.The housing 402 can be constructed of any suitable material, including316 stainless steel, super-duplex stainless steel and Polyether EtherKetone (PEEK). In addition, the housing can be constructed of apiezoelectric material, which will be discussed below.

The housing 402 includes a piston 404 disposed within the housing 402.The piston is movable within the housing 402 along the longitudinal axis406 of the housing 402. A fluid in an environment external to thehousing 402 acts on the piston 404 through an opening 408 in the housing402. In the illustrated embodiment, the housing 402 is located subsea.Accordingly, the hydrostatic pressure of seawater at depth applies aforce on the piston 404, causing the piston 404 to move downward.However, any fluid at pressure suitable for applying a force on thepiston 404 such that the piston 404 moves in such a way that it appliesa compressive force on the piezoelectric element 410 is envisioned.

The piston includes an upper surface 420 and a lower surface 422. Theupper surface 420 area is greater than the lower surface 422 area.Accordingly, any force acting on the upper surface 420 will bemultiplied when the lower surface 422 comes into contact with anothersurface. This is known as “force multiplying.” The piston 404 furtherincludes seals 424 for preventing fluid access into the interior of thehousing 402 beyond the piston.

The housing 402 further includes a piezoelectric transducer 410 composedof a piezoelectric material. Non-limiting examples of suitablepiezoelectric materials include crystals (such as quartz, Berlinite andRochelle salt) and ceramics (such as Lead Zirconate Titanate (PZT),Barium Titanate and Lithium Tantalate). However, any piezoelectricmaterial capable of accumulating an electrical charge in response to anapplied mechanical stress can be used. The piezoelectric transducer 410is disposed below the piston 404. Accordingly, the piezoelectrictransducer 410 is configured to come into physical contact with thepiston 404 when the piston 404 moves downward, thereby applying a forceon the piezoelectric transducer 410. As a result of the PiezoelectricEffect, the piezoelectric transducer 410 produces an electrical charge,or electricity, in response to the load. Owing to the force multiplyingeffect of piston 404, the force acting on the piezoelectric transducer410 will be of greater magnitude than the force acting on the piston404. As the force acting on the piezoelectric transducer 410 isproportional to the electrical charge generated, a greater force willgenerate more electrical charge.

As noted above, the housing 402 can be constructed of a piezoelectricmaterial, in whole or in part. In this instance, the piezoelectricmaterial of the housing would be under constant strain from thehydrostatic pressure of seawater at depth, thereby generating anelectrical charge at all times. The force multiplying piston 404arrangement can still be incorporated into a housing constructed ofpiezoelectric material in order to take advantage of the forcemultiplying effect on electrical charge generation. Alternatively, thehousing could be stand alone, without any piston element.

The generated electrical charge can be passed via wires 412 to anyelectrically powered device or to a capacitor bank for storage. Suchelectrically powered devices or capacitors may be local (e.g., on thehousing 402), or may be remote (e.g., many feet or miles away). In theillustrated embodiment, the electrical charge is passed to anelectronics module 414. The electronics module 414 includes a capacitorbank 416 for storing the generated electricity and a power conditioningunit 418 for improving the quality of the electrical power delivered toother devices.

A top elevation view of an example of the piezoelectric power generatorassembly 400 illustrated in FIG. 4 is shown in FIG. 5. In theillustrated embodiment, the housing 402 is shown to have a circulargeometry. However, other geometries are envisioned. The piston 404 isdisposed concentrically within the housing 402. The opening 408 allows afluid located in an environment external to the housing 402 to act onthe piston 404, causing the piston 404 to move downward. The piston 404further includes seals (424 in FIG. 4) for preventing fluid access intothe interior of the housing 402 beyond the piston.

A cross-section of an example of a piezoelectric power generatorassembly 600 is illustrated in FIG. 6. In the illustrated embodiment,the piezoelectric power generator assembly 600 includes a housing 602.The housing 602 can be constructed of any suitable material, includingstainless steel, super-duplex stainless steel and Polyether Ether Ketone(PEEK). In addition, the housing 602 can be constructed of apiezoelectric material.

The housing 602 includes a piston 604 disposed within the housing 602.The piston is movable within the housing 602 along the longitudinal axis606 of the housing 602. The housing 602 further includes a diaphragm 626disposed above the piston 604. The diaphragm 626 can be composed of anysuitable material, such as Nitrile rubber, natural rubber or Silicone. Afluid in an environment external to the housing 602 acts on thediaphragm 626 through an opening 608 in the housing 602. In theillustrated embodiment, the housing 602 is disposed subsea. Accordingly,the hydrostatic pressure of seawater at depth applies a force on thediaphragm 626, which moves downward and contacts the piston 604, causingthe piston 604 to also move downward. However, any fluid at pressuresuitable for applying a force on the diaphragm 626 such that thediaphragm 626 and piston 604 move in such a way that piston 604 appliesa compressive force on the piezoelectric element is envisioned.

The piston includes an upper surface 620 and a lower surface 622. Theupper surface 620 area is greater than the lower surface 622 area.Accordingly, any force acting on the upper surface 620 will bemultiplied when the lower surface 622 comes into contact with anothersurface. The piston 604 further includes seals 624 for preventing fluidaccess into the interior of the housing 602 beyond the piston. In thisembodiment, the piston 604 is not in direct contact with the fluidlocated in the environment external to the housing 602.

A cross-section of an example of a piezoelectric power generatorassembly 700 is illustrated in FIG. 7. In the illustrated embodiment,the piezoelectric power generator assembly 700 includes a housing 702.The housing 702 can be constructed of any suitable material, includingstainless steel, super-duplex stainless steel and Polyether Ether Ketone(PEEK). In addition, the housing 702 can be constructed of apiezoelectric material.

The housing 702 includes a piston 704 disposed within the housing 702.The piston is movable within the housing 702 along the longitudinal axis706 of the housing 702. Fluid conduit 708 conveys hydraulic fluid tohydraulically actuatable valve block assembly 710. The fluid conduitincludes a T-piece fitting 712 adjacent the valve block assembly 710.The hydraulic fluid acts on the piston 704 through an opening 714 in theT-piece.

The piston includes an upper surface 720 and a lower surface 722. Thelower surface 722 area is greater than the upper surface 720 area. Owingto the force multiplying effect, any force acting on the lower surface722 will be multiplied when the upper surface 720 comes into contactwith another surface. The piston 704 further includes seals 724 forpreventing fluid access into the interior of the housing 702 beyond thepiston.

The housing 702 further includes a piezoelectric transducer 716 composedof a piezoelectric material. Non-limiting examples of suitablepiezoelectric materials include crystals (such as quartz, Berlinite andRochelle salt) and ceramics (such as Lead Zirconate Titanate (PZT),Barium Titanate and Lithium Tantalate). However, any piezoelectricmaterial capable of accumulating an electrical charge in response to anapplied mechanical stress can be used. The piezoelectric transducer 716is disposed above the piston 704. Accordingly, the piezoelectrictransducer 716 is configured to come into physical contact with thepiston 704 when the piston 704 moves upward, thereby applying a force onthe piezoelectric transducer 716. As a result of the PiezoelectricEffect, the piezoelectric transducer 716 produces an electrical charge,or electricity, in response to the load. Owing to the force multiplyingeffect of piston 704, the force acting on the piezoelectric transducer716 will be of greater magnitude than the force acting on the piston704. As the force acting on the piezoelectric transducer 716 isproportional to the electrical charge generated, a greater force willgenerate more electrical charge.

The generated electrical charge can be passed via wires 718 to anyelectrically powered device or to a capacitor bank for storage. Suchelectrically powered devices or capacitors may be local (e.g., on thehousing 702), or may be remote (e.g., many feet or miles away). In theillustrated embodiment, the electrical charge is passed to anelectronics module 725. The electronics module 725 includes a capacitorbank 726 for storing the generated electricity and a power conditioningunit 728 for improving the quality of the electrical power delivered toother devices.

In addition to the embodiments described above, many examples ofspecific combinations are within the scope of the disclosure, some ofwhich are detailed below:

Example 1. A piezoelectric power generator assembly comprising:

-   -   a housing comprising a flow passage defined within the housing;        and    -   a piezoelectric transducer located in the housing and configured        to be in contact with a fluid contained in the flow passage,    -   wherein the piezoelectric transducer is configured to generate        an electrical charge when contacted by the fluid.

Example 2. The power generator assembly of Example 1, wherein the flowpassage has a circular profile and the piezoelectric transducer islocated about the circumference of the flow passage.

Example 3. The power generator assembly of Example 1 further comprisingan electronics module including a capacitor bank.

Example 4. The power generator assembly of Example 1, wherein the fluidis pressurized hydraulic fluid for operating a hydraulically actuatabledevice.

Example 5. The power generator assembly of Example 4, wherein thehydraulically actuatable device is a valve.

Example 6. The power generator assembly of Example 5, the valvecomprising a sensor configured to measure a characteristic of the valve,wherein the sensor is powered by the electrical charge generated by thepiezoelectric material.

Example 7. The power generator assembly of Example 6 further comprisinga storage device including a processor and a memory device capable ofreceiving and storing sensor measurement data.

Example 8. The power generator assembly of Example 7, wherein the valveis configured to adjust between an open position and a closed positionand the characteristic is position of the valve.

Example 9. A piezoelectric power generator assembly comprising:

-   -   a housing;    -   a piezoelectric transducer located in the housing;    -   a piston located in the housing, the piston movable with respect        to the housing and configured to be moved into contact with the        piezoelectric transducer; and    -   wherein the piezoelectric transducer is configured to generate        an electrical charge when contacted by the piston.

Example 10. The power generator assembly of Example 9 further comprisingan electronics module including a capacitor bank.

Example 11. The power generator assembly of Example 9, wherein thepiston is configured to be moved when acted upon by a force external tothe housing, the external force being provided by a fluid at a pressuresufficient for moving the piston.

Example 12. The power generator assembly of Example 11, wherein thefluid is seawater.

Example 13. The power generator assembly of Example 9 further comprisinga diaphragm located in the housing and exposed to an environmentexternal to the housing, wherein the diaphragm is configured to contactthe piston when acted upon by a force external to the housing.

Example 14. The power generator assembly of Example 9, the pistonfurther comprising an upper surface and a lower surface, wherein theupper surface has an area that is greater than an area of the lowersurface.

Example 15. The power generator assembly of Example 9, furthercomprising an electrical device configured to be powered by theelectrical charge.

Example 16. The power generator assembly of Example 15, wherein theelectrical device is located remotely to the housing.

Example 17. The power generator assembly of Example 9, wherein thehousing is constructed of piezoelectric material.

Example 18. A subsea drilling system comprising:

-   -   a subsea blowout preventer stack comprising a hydraulically        actuatable device and a flowline for conveying pressurized        hydraulic fluid to the hydraulically actuatable device; and    -   a piezoelectric power generator assembly comprising:    -   a housing comprising a flow passage defined within the housing;        and    -   a piezoelectric transducer located within the housing and        configured to be in contact with the hydraulic fluid, wherein        the piezoelectric transducer is configured to generate an        electrical charge when contacted by the hydraulic fluid.

Example 21. The power generator assembly of Example 19, wherein thehydraulically actuatable device is a ram.

Example 22. The power generator assembly of Example 20, the ramcomprising a sensor configured to measure a characteristic of the ram,wherein the sensor is powered by the electrical charge generated by thepiezoelectric material.

Example 23. The power generator assembly of Example 21 furthercomprising a storage device including a processor and a memory devicecapable of receiving and storing sensor measurement data.

While the aspects of the present disclosure may be susceptible tovarious modifications and alternative forms, specific embodiments havebeen shown by way of example in the drawings and have been described indetail herein. It should be understood that the disclosure is notintended to be limited to the particular forms disclosed. Rather, thedisclosure is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the disclosure as defined by thefollowing appended claims.

I claim:
 1. A power generator assembly comprising: a housing comprisinga flow passage; a piezoelectric transducer located about a perimeter ofthe flow passage and configured to generate an electrical charge whensubjected to a stress exerted by a fluid pressure of a fluid in the flowpassage; a hydraulically actuatable device and a flow line configured toconvey the fluid to the hydraulically actuatable device, wherein thefluid is pressurized hydraulic fluid for operating the hydraulicallyactuatable device; and a sensor configured to monitor a characteristicof the hydraulically actuatable device, wherein the sensor is powered bythe electrical charge generated by the piezoelectric transducer.
 2. Thepower generator assembly of claim 1, wherein the flow passage has acircular profile.
 3. The power generator assembly of claim 1, furthercomprising an electronics module including a capacitor bank.
 4. Thepower generator assembly of claim 1, wherein the hydraulicallyactuatable device is a valve.
 5. The power generator assembly of claim1, further comprising a storage device including a processor and amemory device capable of receiving and storing sensor measurement data.6. The power generator assembly of claim 4, wherein the valve isconfigured to adjust between an open position and a closed position andthe characteristic is the position of the valve.
 7. The power generatorassembly of claim 1, further comprising: a subsea blowout preventerstack comprising the hydraulically actuatable device and the flowlinefor conveying the fluid to the hydraulically actuatable device.
 8. Thepower generator assembly of claim 7, wherein the hydraulicallyactuatable device is a ram.
 9. The power generator assembly of claim 1,wherein the sensor comprises a hall-effect sensor configured to measurea position of the hydraulically actuatable device.
 10. The powergenerator assembly of claim 1, wherein the sensor is configured tomeasure a temperature at the hydraulically actuatable device, a pressureat the hydraulically actuatable device, or both.
 11. The power generatorassembly of claim 1, wherein the sensor is powered entirely by theelectrical charge generated by the piezoelectric transducer.
 12. Thepower generator assembly of claim 1, comprising a wireless transmitterconfigured to wirelessly transmit sensor data obtained by the sensor toanother location.
 13. The power generator assembly of claim 1,comprising a radio-frequency identification (RFID) tag, wherein the RFIDtag enables transfer of sensor data obtained by the sensor to aremotely-operated vehicle.